In progressive video scanning, successive scanning lines are vertically aligned from frame to frame. For example, in the 1080p/60 standard (1080 scanning lines per frame, 60 frames per second), line 1 of frame 2 is scanned at the same vertical location as is line 1 of frame 1, and so are lines 1 of frames 3, 4, etc. For interlaced video, line 1 of field 2 is vertically located between line 1 and line 2 of field 1, and so is line 1 of field 4, while line 1 of field 3 is vertically coincident with line 1 of field 1.
An interlaced signal is composed of a succession of even and odd fields, two successive fields making a frame. For example, in the 1080i/60 standard (1080 lines interlaced, 60 fields per second), each field is composed of 540 lines, and there are 60 fields or 30 frames per second. A frame is composed of one even field and one odd field in succession.
A progressive scan video signal is composed of horizontal lines drawn consecutively in sequence. In describing aspects of the present invention herein, reference is made to “even” and “odd” lines of a progressive scan video signal, “even” lines being the second line and every other consecutive line (i.e., lines 2, 4, 6, etc.) and “odd” lines being the first line and every other consecutive line (i.e., lines 1, 3, 5, etc.) or vice-versa (in the case of a progressive scan video signal, the designations “even” and “odd” are arbitrary). In cases in which a progressive scan video signal is derived from an interlace scan video signal, “even” lines are typically labeled as those derived from “even” fields and “odd” lines are typically labeled as those derived from “odd” fields.
Interlaced video has been used since the early days of television, and has been slowly falling into disfavor, and replaced by progressive scan for more and more applications, mostly because of the specific needs of computer or computer-like displays. More recent television displays such as LCDs or DLPs can only be driven with a progressive scan. In these cases, interlaced signals have to be de-interlaced, which is costly and difficult.
The main advantages of progressive scan (as compared to interlace scan) are 1) absence of interlace artifacts, such as line twitter, serrations, flicker, etc., 2) ease of processing, from a camera to a display, and 3) ease of digital processing, such as bandwidth or bit-rate compression. The main disadvantage of progressive scan is an increase by a ratio of two of bandwidth requirements, as compared to an interlaced standard having the same field rate as the comparable progressive scan standard.
Digital compression systems require a high bit count (equivalent to large bandwidth) to process the progressive scan video signal with an acceptable quality. The requirements for bandwidth are increasing daily, and the available bandwidth provided by present communication channels is limited. For example, more than 50% of the Internet traffic is occupied by video.
Broadcasters are no longer satisfied with present HDTV standards (1080i and 720p) and would like to move to higher scan rates (e.g., “4K”, which is approximately 2000×4000 pixels) or higher frame rates (120 Hz). Furthermore, interlace standards, which in the past employed analog transmission, reduced the bandwidth requirements by two at the cost of image quality (artifacts). Interlacing does not present such an advantage in compression systems, and is not computer-friendly.
Thus, increased bandwidth, or for a more efficient use of the bandwidth available on different media are required.
Compression standards are slowly improving, getting more efficient in packing an increasing data load into increasingly over-worked channels, but an improvement by a ratio of two in the bandwidth utilization (Mb/s for a constant channel) occurs only every eight to ten years or so.
A need has arisen to reduce the bandwidth of progressive scan video signals while maintaining a reasonable image quality.